1. Technical Field
The present invention relates to a communication terminal of a mobile telephone or the like provided with number keys from 0 to 9 respectively allocated to a plurality of characters, to a character input system that enables efficient input of characters, and to a communication terminal used in a character input system.
2. Related Art
Conventionally, the most common character input method for portable terminal devices such as mobile telephones is the so-called multi-tap method. With the multi-tap method, a number of key operations are required to input a single character.
With a mobile telephone or the like, alphabetic characters are divided up into groups and collected together in groups of three or four characters in alphabetic order, and each group is assigned to a key. For example, the letters A, B and C are allocated to the number key 2, the letters D, E and F are allocated to the number key 3, and so on, as shown in FIG. 2. With mobile phones that are used throughout the world, different character groups may also be allocated to these keys.
As is well known, with character input in the multi-tap method, it is normally necessary to perform more than one key operation to input a single character. For example, to input the word “CAFE”, first of all the number 2 key is pressed three times to input the letter “C”, then the number 2 key is pressed once to input the letter “A”, the number 3 key is pressed three times to input the letter “F”, and finally the number 3 key is pressed twice to input the letter “E”. Therefore, when inputting the word “CAFE”, a total of nine key operations are required, namely the sequence of pressing the number keys “222,2,333,33”. With the multi-tap method, they are five more operations than performing the same input using a personal computer keyboard. This type of multi-tap method character input places a large burden on the user, and ambiguous key input methods have been proposed to improve this situation.
The basic concepts for determining a correct input character sequence or word for an ambiguous key input are summarized in the article “Probabilistic Character Disambiguation for Reduced Keyboards Using Small Text Sample” published in 1992 by the Journal of the International Society for Augmentative and Alternative Communication, by John L. Arnott and Muhammed Y. Javad (hereinafter referred to as the “Arnott article”). The Arnott Article points out that the majority of disambiguation methods use already known statistics for character strings or words of the relevant language to resolve ambiguity in a character string or word of a given context. Specifically, current disambiguation systems perform statistical analysis of a user's ambiguous key input and determine an appropriate interpretation for the ambiguous key input.
A disambiguation system called T9.RTM is also being developed by Tegic Communications, Inc.). This system checks a user's ambiguous key input against a language database, and is disclosed in U.S. Pat. No. 5,818,437. In U.S. Pat. No. 6,223,059, Nokia Mobile Phone Limited has proposed a mobile device containing a predictive editor function to further improve the input efficiency of a mobile telephone type keypad.
FIG. 12 is a drawing showing the system configuration of a mobile telephone provided with a disambiguation system. This system is comprised of a central processing unit (CPU) 200, and peripheral devices such as a memory 201, keypad 202, display 203, speaker and microphone 204, and transceiver circuit 205. The CPU 200 reads data from the memory 201 and executes instructions. The instructions are generated by the following software programs: operating system 206, browser or e-mail program 207, another application program 208, and disambiguation software 209. A character string database 210 also resides in the memory 201. With a mobile telephone provided with this type of disambiguation system, it is possible for a user to input character strings or words through ambiguous key input. The disambiguation software 209 checks whether a character string or word that can be constructed from an inputted ambiguous character string exists in the database 210. A character string database built-into the mobile telephone is difficult to update, but the character string database is normally a word database, and requirements for updating data are not particularly stringent. However, it is not appropriate to build in a character string database for data that is added or updated every day, such as domain names.
The disambiguation systems proposed up to now, however, have all been integrated into a portable terminal device. At the present time, disambiguation systems are not being incorporated into the majority of portable terminal devices available on the market, and with these majority of portable terminal devices the only usable input method is the multi-tap method. Also, in the case where a disambiguation system is incorporated into a portable terminal device, it is not easy to update the character string database within the device. For example, in cases where data update is carried out daily, such as domain names, database updating is difficult